From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Robinson Subject: Re: Poor write performance with write-intent bitmap? Date: Wed, 22 Apr 2009 13:41:49 +0100 Message-ID: <49EF108D.4070605@anonymous.org.uk> References: <49ED096E.1000002@anonymous.org.uk> <49ED16F7.3040906@anonymous.org.uk> <4081b80da35818efbc07723240f8ea36.squirrel@neil.brown.name> <49ED2BC3.7050109@anonymous.org.uk> <87d4b5m4kf.fsf@frosties.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87d4b5m4kf.fsf@frosties.localdomain> Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: Linux RAID List-Id: linux-raid.ids On 22/04/2009 10:16, Goswin von Brederlow wrote: > John Robinson writes: >> Can't do that, my root filesystem is on the RAID-5, and part of the >> reason for wanting the bitmap is because the md can't be stopped while >> shutting down, so it was always wanting to resync at startup, which is >> rather tedious. > > Normal shutdown should put the raid in read-only mode as last step. At > least Debian does that. That way even a mounted raid will be clean > after reboot. Yes, I would have thought it should as well. But I've just looked at CentOS 5's /etc/rc.d/halt and as far as I can see it doesn't try to switch md devices to read-only. Of course the root filesystem has gone read-only but as we know that doesn't mean the device underneath it gets told that. In particular we know that ext3 normally opens its device read-write even when you're mounting the filesystem read-only (iirc it's so it can replay the journal). Another issue might be the LVM layer; does that need to be stopped or switched to read-only too? > I would also suggest restructuring your system like this: > > sdX1 1GB raid1 / (+/boot) > sdX2 rest raid5 lvm with /usr, /var, /home, ... > > Both / and /usr can usualy be read-only preventing any filesystem > corruption and raid resyncs in that part of the raid. I did do this multiple partition/LV thing once upon a time, but I got fed up with having to resize things when one partition was full and others empty. The machine is primarily a fileserver and Xen host, so the dom0 only has 40GB of its own, and I couldn't be bothered splitting that up. Having said all this, your suggestion is a good one, it's just my preference to have it otherwise :-) Cheers, John.